I'm pretty little -- I am here now -- that -- -- the -- ABC family show. And it is a huge tonight on this show ladies we want to know all about that first let me introduce everybody TO. We have with us Lucy Hale Shay Mitchell and -- -- in Venice Ariel. -- when you guys all the scraps. Had -- -- did today was on the I think I'll. It's sort of had a different theory but we didn't know -- like we're right along the audience they didn't -- this script until. The day before we started shooting it -- and and that retail all of us had different light facial expressions are like. No I knew it well like yeah but it was crazy well yeah. You'll explained because we have a little peace to show you what we're talking about. This is the question pretty little liars fans have been asking since day one clueless is daddy guys. I figured out for the past two seasons of the wildly popular ABC family hit. This mysterious a character has made the lives of the shows forty heroines -- Spencer Harris and Emily and -- living nightmare. Including ground -- a twisted game of lives blackmail and of course it's. Many don't have. Those threatening text messages. -- too much. It's a mystery sparked an episode one after the -- queen B Alison. Mysteriously vanished willing to prominence in the girl swore they'd never tell anyone what really happened the night of her disappearance. But that didn't stop bay from knowing every intimate detail don't know everything. So who is day -- night the village will finally be exposed -- I love it and Uday is right TV show may have a very different. Yeah answer to -- as I was -- about Michelle -- that it can go either way and that's exactly citing. You guessed what do you guys did you guess right woody -- -- -- -- -- -- -- I was -- of a very proud Spencer moment because I've looked more like two seasons had my theory is in kind of been running smartly. Usually the I -- now of course but I think he -- you know I'm always alone in the woods trying to figure out who is and it isn't very -- that. Quiet moment of like. Relief and excitement -- when we -- this -- but I tend to pay the debt it's. True that there could actually be more than one day. Well I think what's so exciting about this storyline is that McCain is everywhere and I don't know if it's possible rating be just one person accomplish all that. But literally could go and so many different activity gives me one person -- the extremely. High intelligence and -- are valid or it can be -- small town that I wouldn't trust anything that night. Let me ask you do you think it. Or what do you -- it's because need to show such ahead of -- you can see the audience how the site they are here. And it's it's the most read about show. On his right now yeah incredible and I mean we just got back from Rio and rebel and it was -- -- for the -- -- the fact that it is so relatable. They didn't immediately I mean you don't hear about one nagging -- little bit of -- yeah. And -- Livingston and their relationship so I think the fact that that everybody can relate to -- I know there's also been a lot of talk you guys have dealt with bullying we talk about that would Lady Gaga. -- have you heard from teens. Appreciating reaching out to you all about the story lines I mean -- Eddie -- especially saying his you know I'm prepared I think he felt like. Death to -- every time I've heard it -- Even people coming at me on the street it and I'm really means that he. Not only -- -- -- entertaining but just how much it's actually impacted a lot of girls and boys -- you know it it's amazing Kenya. Why were clearly not -- give it up we're gonna tell you lay as its next big like you. All have brought a -- -- our audience and yet you mind sharing with us each ship a New York clues are you ready eager to clues. Well it's not like -- but I'll give you can't pay below this one of the PLLs more than the -- yeah. Okay alone. Nixon you -- OK and you didn't know. I had been detected by eight evil yeah. And -- repeat that. And hasn't voted to justify his evil. I didn't -- -- actually did I don't know I didn't learn that colon cousin -- yeah. Read his friends are going to be torturing human herself -- Awards -- this is TV ads I don't I think it's having -- totally impossible. Let you do you want to get a clue for you think you suspects -- though I am but apparently I don't know what I had -- riot. Not. The -- that I have to give everybody is that pays. Admires. One of the PLO is more than any other way. It is a conundrum we will find out tonight everybody. And I dropping -- -- a -- that little bar yeah. Yeah. And yeah yeah. Yeah I'm I'm a big zero residents might -- I love my lovely -- in the right job and -- -- let you know. And that's -- -- -- -- that -- got here and I love your -- yet stylish your hands they knew why stars of the biggest show on TV. Yeah. And Atlantic will be one of our issues I don't know what guys I hate to have the countdown now that it not look at. Yeah. But -- have the best season finale very little liars airs tonight 8 eastern. The exhibit at ABC Bentley can can -- yeah. -- -- -- Got a real problem with the show we've got a real problem with this and that -- the name that -- Gorgeous little -- --

This transcript has been automatically generated and may not be 100% accurate.

Now Playing: Shay Mitchell of 'Pretty Little Liars'

Now Playing: Star-Studded Premiere for "The Tonight Show Starring Jimmy Fallon"